The goal of this work is the elucidation of the mechanisms controlling the rate of protein synthesis at the cytoplasmic level in mammalian cells. The tissue utilized in the present studies is the Ehrlich ascites tumor cell growing in suspension culture. This cell demonstrates cytoplasmic control mechanisms which respond vigorously to alterations in nutrient (essential amino acid, glucose, or serum) concentration in the medium. We have recently demonstrated that upon nutrient deprival one such mechanism operates to inhibit polypeptide chain initiation by inhibiting an early step in polypeptide chain initiation, namely the binding of Met-tRNAf, the initiating aminoacyl tRNA, to the native 40s ribosomal subunit. This step requires eucaryotic initiation factor 2 (eIF-2), which, together with Met-tRNAf and GTP form a ternary complex. We are presently examining factors affecting ternary complex formation. We find a soluble inhibitor of complex formation, and a soluble protein which prevents this inhibition. We are comparing the affects of these factors upon phosphorylated and unphosphorylated eIF-2.